1. It's a good thing to play with a metronome, it increases the quality of your playing (you develop your skill by keeping the beat).
2. The metronome DOES NOT make you play faster automatically.
3. The metronome helps you speeding up. How?
You increase the tempo and there will always be a spot where it goes too fast and you start making mistakes.
Take the tempo back again to the fastest that you can play without mistakes. But most importantly : look at the mistakes you made while playing a bit faster and try to figure out what was the problem: most frequently it's the way you use your pick (upstrokes, downstrokes, sweep,...). Maybe there's a better/easier (and hence faster) way to play that part of the music. Study that untill it's perfect.
4. Increase the speed of the metronome again untill you discover the next "mistake" and use the same method over and over again.
So, to put it different: use the metronome as a tool to discover the "weak spot" in your playing and speed it up...